The present invention relates to a method and for simultaneously molding portions of a separable article, more particularly such a method and apparatus for molding objects of revolution made from composite material.
Gas turbine engines for aeronautical applications, such as turbofan engines, and turbojet engines both with and without afterburners typically have an exhaust duct which is made of a metallic material, such as a titanium. In such aeronautical applications, it is highly desirable that all parts of the aircraft, including the power plant, be as light in weight as possible in order to increase the performance of the aircraft, and to make it more efficient. Titanium has been typically selected as the material for the engine exhaust gas duct due to its relatively high strength and relatively low weight.
The weight of the engine assembly could be further reduced by making this duct out of a composite material, rather than a metallic material, such as titanium. However, the production of such an article has encountered heretofore insurmountable problem. In order to obtain access to the internal components of the engine, the exhaust duct must be comprised of at least two sections, which are separable in order to permit such access.
French Patent 2,490,993 describes the molding of a hollow body from laminated material in which the mold consists of at least two mold portions which define a molding cavity which has the outside shape of the hollow body to be molded. This patent also discloses the use of an expansible pouch or bag located within the molding cavity whose external shape corresponds to the inside shape of the hollow molded body. The process described in this document consists of separately covering each mold portion with a pre-impregnated composite mat (prepreg) or by impregnating the fabric portion of the composite material with a resin after placing it into the mold portions. The mold portions are then assembled together with the expansible pouch located within the mold. By increasing the temperature of the mold assembly, the expandable pouch is expanded to thereby press the impregnated composite material against the wall of the mold portions and the composite material is cured. Although this method allows making complex shaped hollow articles, such as pipes, tubes, or the like, it does not describe the making of such an object comprising separable portions.
Obviously, it would be feasible to manufacture the two separate portions of the article separately in different molds. However, in order to ensure that the separate portions of the article have identical properties, it is mandatory that they be manufactured simultaneously in the same mold.